Many children with no signs of respiratory infection tested positive for Mycoplasma pneumoniae, suggesting that such tests may be unreliable for clinical diagnosis, researchers said.

Among 405 children asymptomatic for respiratory infections screened for M. pneumoniae DNA, 21.2% (95% CI 17.2%-25.2%) had positive results -- a higher percentage than in 321 children with symptoms of respiratory infection, of whom 16.2% (95% CI 12.2%-20.2%) tested positive, according to Emiel B.M. Spuesens, MD, of Erasmus Medical Center in Rotterdam, Netherlands, and colleagues.

"This finding is important as it implies that the daily clinical practice of diagnosing M. pneumoniae respiratory tract infection (RTI) is inadequate," the researchers wrote online in PLoS Medicine. "Specifically, it does not seem appropriate to use the detection of M. pneumoniae in the upper respiratory tract by polymerase chain reaction (PCR) [detection technology] as a method to diagnose symptomatic RTIs caused by this bacterium."

Spuesens and colleagues added, "A diagnosis of M. pneumoniae-induced respiratory tract disease cannot be based exclusively on serology or the detection of M. pneumoniae DNA in the upper respiratory tract, and caution should be taken in the interpretation of diagnostic tests for M. pneumoniae."

Diagnosis of RTIs is often tricky and clinicians have come to rely on microbial diagnostic tests, including serology tests as well as direct PCR-based detection of potentially pathogenic organisms, the researchers observed. M. pneumoniae is of special concern because it has been linked to as many as one-third of community-acquired pneumonia cases seen in children.

Currently, diagnosis of M. pneumoniae infections "relies on the detection of either serum antibodies against [the organism] or bacterial DNA in samples of the upper respiratory tract," Spuesens and colleagues wrote, sanctioned by guidelines from the Infectious Diseases Society of America and other groups.

Yet, the possibility that children may harbor M. pneumoniae without clinical infection -- as occurs with other pathogens such as Staphylococcus aureus -- has not been examined until now, the researchers indicated.

To fill this gap, Spuesens and colleagues recruited two groups of children ages 3 months to 16 years from 2008 to 2011 for serological and PCR-based M. pneumoniae testing. One group consisted of children with no sign of respiratory disease who were scheduled for elective surgery at Erasmus Medical Center's short-stay center. The other was children being seen for suspected respiratory infection at Erasmus's emergency department or its after-hours primary care clinic.

Blood samples and upper respiratory swabs were taken from all children. Those testing positive either on serology or PCR were then invited for monthly follow-up, with molecular testing at each visit until results were negative for M. pneumoniae.

The researchers found that neither serological nor molecular testing yielded positive results more often in symptomatic versus asymptomatic participants. Nor was there any apparent difference in the locations of M. pneumoniae colonization in the respiratory tract, i.e., pharyngeal versus nasopharyngeal, between groups.

Results also indicated that multiple pathogens were commonly present in both groups of children. With data on tests for bacterial or viral pathogens besides M. pneumoniae available in 112 of the asymptomatic group and 90 of the symptomatic group, 56% of both groups tested positive for at least two pathogens.

Among those positive for M. pneumoniae carriage, 21 asymptomatic and 22 symptomatic children participated in the longitudinal follow-up. Spuesens and colleagues found that, in most cases, the bacterium's presence was relatively short-lived. Results were negative after the first month in 15 of the asymptomatic group and 19 of the symptomatic group.

In the remaining minority, persistence of M. pneumoniae was documented for up to 4 months. A few children in each group tested negative at one point but positive again at a later test.

Limitations to the study included its single-center design, small sample size, and use of serology testing for some data, positive results for which could reflect past exposure rather than current carriage of M. pneumoniae.

Funding sources for the study included the Netherlands Organization for Health Research and Development and the European Society for Paediatric Infectious Diseases.

One author had been on Cepheid's advisory board and subsequently joined bioMerieux after the study was completed. Others reported relationships with Viroclinics Biosciences and Abbott.

Reviewed by Robert Jasmer, MD Associate Clinical Professor of Medicine, University of California, San Francisco and Dorothy Caputo, MA, BSN, RN, Nurse Planner

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